1. Field of the Invention
The present invention relates to furnace control apparatus, and more particularly, to means for detecting the existence of a dangerous condition of fuel combustion in a furnace.
2. Prior Art
It is well known that malfunctioning furnaces can create an explosive situation which may result in severe damage to the furnace and even the dwelling or other structure in which it is housed. Many devices have been designed for detecting certain well known conditions which can create such an explosive condition within a furnace.
For example, devices such as that disclosed by Hobbs U.S. Pat. No. 2,874,763 and Fehrenbach U.S. Pat. No. 2,283,496, are intended to detect the absence of a flame within the furnace and as a result shut off fuel supply to the furnace so that an excess of fuel does not accumulate in the bottom of the furnace which might otherwise result in an explosion upon subsequent ignition. In addition, Hobbs discloses a system for shutting off the pilot light and main fuel supply lines in order to prevent additional accumulation of fuel within the furnace. A further control feature of Hobbs prevents ignition of the pilot light when a heavy mist or smoke condition exists within the furnace chamber.
However, such devices although effective in sensing the absence of a flame or the presence of a dangerous condition existing within the furnace prior to ignition, can still permit continuous operation of the furnace, particularly oil burning furnaces and the like, under circumstances which can cause severe smoke damage to a dwelling. Such a condition can exist, for example when the air supply to the furnace combustion chamber is insufficient to permit complete combustion of the fuel. Under such circumstances, although the furnace will continue to operate, substantial amounts of smoke will be produced which can be expelled from openings in the furnace other than the flue and thus not only cause substantial damage to the building and furnishings, but also constituting severe hazard to the life and health of the occupants.
The use of well known smoke detecting devices which provide an alarm, for example, such as disclosed in Webb U.S. Pat. No. 4,004,288 and Franks U.S. Pat. No. 4,001,800, can provide an alert to the presence of such a dangerous condition existing in the furnace when smoke is unnaturally expelled therefrom into the room containing the furnace. However, unknolwedgeable home owners, for example, would not be aware of the necessity of turning off the fuel supply in order to stop the smoke emmission, and therefore such devices are generally unsatisfactory for such an application.